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Kustom wanna-be-tube

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Hello all you lovers of tube* amp's,

already been discussed about this little quirky amp
so not to go back to that topic what is too difficult (read: technical) for me to apply all-or-some of mod's,
I went for the very first and easiest mod: replaced ax7 with au7 lamp.

Now is Gain more controllable and that typical rattling is gone.
It sounds really good. Removed the head and running it with Roland's external cab.
Happy days ..

Schematic was a problem as I can read it so I found one. 

I would like to apply Gain to the clean channel so if someone know-to ..  my eyes  are wide open.

tube* - well it's a hybrid.


Hi Lex,,
You can only do that with a 2 channel circuit.
your unit is single channel with switching for OD as such whatever changes you make effects both clean and drive.

If it's feasible you could separate SW1B from SW1A into 2 separate switches then on clean just open SW1B will remove diodes from the circuit.
As the diodes are the main source of distortion then removing them with SW1A still engaged in drive mode the signal will be a lot cleaner.
How well that would work in practice is anyone's guess.

One thing I have learned in many years of trying to refine multi channel circuits is the balance between Clean and Drive is ever so hard to get right. :grr :grr :grr
Very few Amps I've had the pleasure and often Displeasure of using are NOT well balanced. It took me years of building dud circuits and amp mods ,, to finally realize that as much as I hate pedal boards I now use them as it's so much easier to work into a clean amp and do all the tricks on the pedal boards.

I'm now quite happy with my setup and hardly ever bother to tweak the amp. 8|
At least half of my setup is all my own designs as I've learned from years of research what works,,, a long road but all done on a budget. :tu:

Hi Phil, thanx,

Im getting what you wrote, this about single / double circuit is logical to me.

I was thinking that the easy solution would be to make a switch to clipping diodes.
However, from the factory those 4 diodes are covered in some white plastic/hard glue.
Like they want to prevent people modifying it.
I suppose it would be possible to melt that stuff with soldering iron.

But also, just to try OD channel without clipping diodes Im thinking to 'jump' them instead of removing them from the circuit (much less work).
Is this something as DO it or NO No nooo ...  cant imagine that I could burn something as is the same thing as removing diodes all together and placing a jumper.

OD channel with gain on 0 behaves as the clean channel.

Im keeping everything on 'the budget' side while learning. Im not expecting huge changes, but even little ones will boost my enthusiasm.

Of course pedals are the way to go, thats clear to me.


No don't bridge the diodes that will just leave the 1k5 resistor (R14) across the audio path.
Likely low volume will be the result.

Removing means open circuit which is the complete opposite of jumpering them with a wire, closed circuit.

Likely easier to replace R14 with a pot and dial in how much diode effect (distortion) you want.
I don't know how well that would work but I'd guess somewhere between 10k up to 100k pot would work.

ok Phil, learned something again, 

That something is actually - im getting more confused what is a clear sign of my elec knowledge around amp circuits.

Does it work like this;
- SW1A (Gain) is ON > so it gives the power trough 2 > then trough the tube V1A > and then sends it to 1 > and further to the tone stack?
- signal goes back to the tube > V2A > amp > speaker ?
- if this is correct, I cant see from the circuit how OD works only when Gain is on

about the pot - well sins I started being interested how an amp works, been thinking of: "why is there only off-on switch for OD instead of a pot.."
So you gave me a good idea that I should try to implement.

Thanx for the time and willing to explain stuff,



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